
<PAGE>   1

                                    GUARANTY


         THIS GUARANTY is entered into as of this 31st day of March, 1995 by
Neuromed, Inc., a Florida corporation ("Guarantor"), in favor of NationsBank of
Texas, N.A. ("Lender") under the First Amended and Restated Credit Agreement
dated as of March 31, 1995 (such agreement, together with all amendments and
restatements thereof, the "Credit Agreement") between Quest Medical, Inc.
("Borrower") and Lender.


                                   RECITALS:

         Pursuant to the Credit Agreement and the other Loan Papers, Borrower
may from time to time be indebted to Lender; and

         Lender is not willing to make Advances under the Credit Agreement or
otherwise extend credit to Borrower unless Guarantor unconditionally guarantees
payment of all present and future indebtedness and obligations of Borrower to
Lender; and

         Guarantor is a wholly-owned subsidiary of Borrower and will directly
benefit from Lender's making loans to Borrower.


                                   AGREEMENT:

         NOW, THEREFORE, as an inducement to Lender to enter into the Credit
Agreement and to make loans to Borrower thereunder, and to extend such
additional credit as Lender may from time to time agree to extend, and for
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the parties do hereby agree as follows:

         Guarantor hereby unconditionally guarantees to Lender the prompt
payment at the time provided inSection 5 of this Guaranty, at maturity (by
acceleration or otherwise), and at all times thereafter, of the Guaranteed
Indebtedness (hereinafter defined), this guaranty being upon the following
terms and conditions:

         1.      Definitions.  Unless defined herein, all capitalized terms
have the meanings ascribed to such terms in the Credit Agreement.  As used
herein, the following terms are defined as follows:

         "Borrower" includes, without limitation, Borrower, Borrower as a
         debtor-in-possession, and any receiver, trustee, liquidator,
         conservator, custodian, or similar party appointed for Borrower or all
         or substantially all of its assets pursuant to any Debtor Relief Law.

         "Guaranteed Indebtedness" means any and all obligations now or
         hereafter existing of Borrower, each other Obligor and any other
         Person under the Credit Agreement and the other Loan Papers, including
         any extensions, modifications, substitutions, amendments and renewals
         thereof, whether for principal, interest,
<PAGE>   2
         fees, premium, expenses, indemnification or otherwise (all such
         obligations of Borrower and each other Obligor being the
         "Obligations"), together with all amounts which constitute part of the
         Obligations and would be owed by Borrower or any other Person to
         Lender under any Loan Paper, but for the fact that they are
         unenforceable or not allowable due to the existence of a bankruptcy,
         reorganization or similar proceeding involving Borrower, each other
         Obligor or any other Person (including all such amounts which would
         become due but for the operation of the automatic stay under Section
         362(a) of the United States Bankruptcy Code, 11 U.S.C. Section 362(a),
         and the operation of Sections 502(b) and 506(b) of the United States
         Bankruptcy Code, 11 U.S.C. Section 502(b) and Section 506(b) or any
         analogous stay under any foreign Law), and any and all costs,
         attorneys' fees, and expenses incurred by Lender by reason of
         Borrower's, Guarantor's or any other Person's default in payment of
         any of the foregoing indebtedness.

         "Maximum Guaranteed Indebtedness" means, with respect to Guarantor as
         of the date of determination, the lesser of (a) the Guaranteed
         Indebtedness, and (b) the maximum amount for which Guarantor may be
         liable under this Guaranty without such amount and Guarantor's
         obligations under this Guaranty with respect to such amount being
         deemed a fraudulent transfer, as determined by a bankruptcy or similar
         court.

         2.      Maximum Guaranteed Indebtedness.  Notwithstanding any contrary
provision herein or in any other Loan Paper, Guarantor's maximum liability
hereunder shall not exceed the Maximum Guaranteed Indebtedness.  Guarantor
agrees that the Guaranteed Indebtedness may at any time exceed the aggregate
Maximum Guaranteed Indebtedness of all Obligors (excluding Borrower) on all or
any part of the Guaranteed Indebtedness, without affecting or impairing the
obligation of Guarantor.

         3.      Continuing Guaranty.  This instrument shall be an absolute and
continuing guaranty of payment, and the circumstances that at any time or from
time to time the Guaranteed Indebtedness may be paid in full shall not affect
the obligation of Guarantor with respect to indebtedness or obligations of
Borrower to Lender thereafter incurred pursuant to the Credit Agreement, any
other Loan Paper, or otherwise.

         4.      Other Debt.  If Guarantor becomes liable for any indebtedness
owing by Borrower to Lender by endorsement or otherwise, other than this
Guaranty, such liability shall not be in any manner impaired or affected
hereby, and the Rights of Lender hereunder shall be cumulative of any and all
other Rights which Lender may ever have against Guarantor.  The exercise by
Lender of any Right or remedy hereunder or under any other instrument shall not
preclude the concurrent or subsequent exercise of any other Right or remedy.

         5.      Payment.  If an Event of Default exists, Guarantor shall, on
demand by Lender and without further notice of dishonor, without any notice
having been given to Guarantor previous to such demand of acceptance by Lender
of this Guaranty, and without any notice having been given to Guarantor
previous to such demand of the creating or incurring of the Guaranteed
Indebtedness, pay the entire amount of the Guaranteed Indebtedness to Lender at
the Principal Office of Lender, and it shall not be necessary for Lender, in
order to enforce such





                                      -2-
<PAGE>   3
payment by Guarantor, first to institute suit or exhaust its remedies against
Borrower, or other Person liable for the Guaranteed Indebtedness, or to enforce
its Rights against any security which shall ever have been given to secure the
Guaranteed Indebtedness, this Guaranty being a guaranty of payment and not of
collection, and in no way conditional or contingent.  Guarantor hereby
irrevocably and unconditionally covenants and agrees that it is liable for the
Guaranteed Indebtedness as primary obligor.

         6.      Obligation Not Impaired.  Guarantor hereby agrees that its
obligations under the terms of this Guaranty shall not be released, diminished,
impaired, reduced, or affected by the occurrence of any one or more of the
following events:  (a)  the taking or accepting of any other security or
guaranty for any or all of the Guaranteed Indebtedness; (b) any release,
surrender, exchange, subordination, or loss of any security at any time
existing in connection with any or all of the Guaranteed Indebtedness; (c) the
modification of, amendment to, or waiver of compliance with any terms of the
Credit Agreement or any other Loan Paper without the notification of Guarantor
(the right to such notification being herein specifically waived by Guarantor);
(d) the insolvency, bankruptcy, or lack of corporate or other power of Borrower
or any other Person at any time liable for the payment of any or all of the
Guaranteed Indebtedness, whether now existing or hereafter occurring; (e) any
renewal, extension, and/or rearrangement of the payment of any or all of the
Guaranteed Indebtedness, either with or without notice to or consent of
Guarantor, or any adjustment, indulgence, forbearance, or compromise that may
be granted or given by Lender to Borrower, Guarantor or any Person at any time
liable for the payment of any or all of the Guaranteed Indebtedness; (f) any
neglect, delay, omission, failure, or refusal of Lender to take or prosecute
any action for the collection of any of the Guaranteed Indebtedness or to
foreclose or take or prosecute any action in connection with any instrument or
agreement evidencing or securing all or any part of the Guaranteed
Indebtedness; (g) any failure of Lender to notify Guarantor of any renewal,
extension, or assignment of the Guaranteed Indebtedness or any part thereof, or
the release of any security, or of any other action taken or refrained from
being taken by Lender, it being understood that Lender shall not be required to
give Guarantor any notice of any kind under any circumstances whatsoever with
respect to or in connection with the Guaranteed Indebtedness; (h) the
unenforceability of all or any part of the Guaranteed Indebtedness against
Borrower or any Person at any time liable for the payment of any or all of the
Guaranteed Indebtedness by reason of the fact that the Guaranteed Indebtedness,
and/or the interest paid or payable with respect thereto, exceeds the amount
permitted by Law, the act of creating the Guaranteed Indebtedness, or any part
thereof, is ultra vires, or the officers creating same acted in excess of their
authority, or for any other reason; or (i) any payment by Borrower to Lender is
held to constitute a preference under any Debtor Relief Law or if for any other
reason Lender is required to refund such payment or pay the amount thereof to
another Person.

         7.      Waivers.  Guarantor hereby waives all Rights by which it might
be entitled to require suit on an accrued right of action in respect of any of
the Guaranteed Indebtedness or require suit against Borrower or others, whether
arising pursuant to Section 34.02 of the Texas Business and Commerce Code, as
amended, Section 17.001 of the Texas Civil Practice and Remedies Code, as
amended, and Rule 31 of the Texas Rules of Civil Procedure, as amended, or
otherwise.





                                      -3-
<PAGE>   4
         8.      Guarantor Insolvency.  Should Guarantor become insolvent, fail
to pay its debts generally as they become due, voluntarily seek, consent to, or
acquiesce in the benefits of any Debtor Relief Law or become a party to or be
made the subject of any proceeding provided for by any Debtor Relief Law (other
than as a creditor or claimant) that could suspend or otherwise adversely
affect the Rights of Lender granted hereunder, then, the Guaranteed
Indebtedness shall be, as between Guarantor and Lender, a fully matured, due,
and payable obligation of Guarantor to Lender (without regard to whether
Borrower is then in default under the Credit Agreement or any other Loan Paper
or whether any part of the Obligation is then due and owing by Borrower to
Lender), payable in full by Guarantor to Lender upon demand, which shall be the
estimated amount owing in respect of the contingent claim created hereunder.

         9.      Representations and Warranties.  Guarantor represents and
                 warrants to Lender that:

                 (a)      Guarantor is a corporation duly organized and validly
         existing under the Laws of the State of Florida;

                 (b)      Guarantor is qualified to do business in all
         jurisdictions where the nature of its business or properties require
         such qualification;

                 (c)      the board of directors of Guarantor has duly
         authorized the execution, delivery, and performance of this Guaranty
         and the other Loan Papers to be executed by Guarantor and no consent
         of any shareholder of Guarantor is required to authorize such
         execution, delivery or performance;

                 (d)      Guarantor has full legal right, power, and authority
         to execute, deliver, and perform under this Guaranty and the Loan
         Papers to be executed and delivered by it;

                 (e)      this Guaranty and the other Loan Papers to be
         executed by Guarantor constitute the legal, valid, and binding
         obligations of Guarantor enforceable in accordance with their terms
         (subject as to enforcement of remedies to any applicable Debtor Relief
         Laws);

                 (f)      the execution or delivery of any Loan Papers to be
         executed by Guarantor and performance thereunder, does not conflict
         with, or result in a breach of the terms, conditions, or provisions
         of, or constitute a default under, or result in any violation of, or
         result in the creation of any Lien upon any properties of Guarantor
         (other than rights of setoff in favor of Lender) under, or require any
         consent (other than consents already obtained), approval, or other
         action by, notice to, or filing with any Tribunal or Person pursuant
         to, the corporate governance documents of Guarantor, any award of any
         arbitrator, or any agreement, instrument, or Law to which Guarantor or
         any of its properties is subject;

                 (g)      the financial statements of Guarantor and its
         subsidiaries dated January 31, 1995 delivered to Lender fairly present
         its financial condition and the results of operations as of the dates
         and for the periods shown, all in accordance with GAAP





                                      -4-
<PAGE>   5
         (subject to audit adjustments) and such financial statements reflect
         all material liabilities, direct and contingent, of Guarantor that are
         required to be disclosed in accordance with GAAP (subject to audit
         adjustments);

                 (h)      as of the date of such financial statements, there
         were no contingent liabilities, liabilities for Taxes currently due
         and payable, forward or long-term commitments, or unrealized or
         anticipated losses from any unfavorable commitments that are
         substantial in amount and that are not reflected on such financial
         statements or otherwise disclosed in writing to Lender;

                 (i)      Guarantor is Solvent;

                 (j)      there is no pending or, to Guarantor's best
         knowledge, threatened Litigation or any claim related to the release
         of any toxic or hazardous waste or substance or alleged violation of
         any federal, state or local environmental, health or safety law
         against Guarantor that could constitute a Material Adverse Change as
         to Guarantor;

                 (k)      the value of the consideration received and to be
         received by Guarantor is reasonably worth at least as much as the
         liability and obligation of Guarantor hereunder, and such liability
         and obligation may reasonably be expected to benefit Guarantor
         directly or indirectly;

                 (l)      Guarantor is familiar with, and has independently
         reviewed books and records regarding, the financial condition of
         Borrower and is familiar with the value of any and all collateral
         intended to be created as security for the payment of the Guaranteed
         Indebtedness; and

                 (m)      neither Lender nor any of its officers or agents has
         made any representation, warranty or statement to Guarantor in order
         to induce Guarantor to execute this Guaranty.

         10.     Affirmative Covenants.  So long as any of the Facility A
Commitment or the Facility B Commitment or any Advance under the Credit
Agreement or any portion of the Obligation is outstanding, or Borrower owes any
amount under any Loan Paper, Guarantor:

                 (a)      shall furnish to Lender:

                               (i)         As soon as available and in any
                 event within 45 days after the end of each of Guarantor's
                 fiscal quarters, consolidated and consolidating balance sheets
                 of Guarantor as of the end of such quarter, and consolidated
                 and consolidating statements of income, and a consolidated
                 statement of changes in cash flow of Guarantor and its
                 subsidiaries for such quarter and for the portion of the
                 fiscal year ending with such quarter, setting forth, in
                 comparative form, figures for the corresponding periods in the
                 previous fiscal year, all in reasonable detail, and certified
                 by an authorized officer of Guarantor as prepared in





                                      -5-
<PAGE>   6
                 accordance with GAAP, and fairly presenting the financial
                 condition and results of operations of Guarantor and its
                 subsidiaries;

                              (ii)         As soon as available and in any
                 event within 90 days after the end of each fiscal year of
                 Guarantor, a consolidated balance sheet of Guarantor and its
                 subsidiaries as at the end of such fiscal year, and
                 consolidated statements of income and changes in cash flow of
                 Guarantor and its subsidiaries for such fiscal year, all in
                 reasonable detail, prepared in accordance with GAAP, and
                 accompanied by an unqualified opinion of the auditor, which
                 opinion shall state that said financial statements were
                 prepared in accordance with GAAP, that the examination by the
                 auditor in connection with such financial statements was made
                 in accordance with generally accepted auditing standards, and
                 that said financial statements present fairly the financial
                 condition and results of operations of Guarantor and its
                 subsidiaries;

                             (iii)         Promptly upon becoming aware,
                 written notice of any actual or potential contingent
                 liabilities, including Litigation, against Guarantor involving
                 liability in an amount which must be disclosed in either
                 Borrower's or Guarantor's financial statements or filings with
                 the Securities and Exchange Commission;

                              (iv)         Promptly after filing or receipt
                 thereof by an  officer of Guarantor, copies of all reports and
                 notices that Guarantor or any of its Subsidiaries furnishes to
                 or receives from any holders of any Debt or Contingent
                 Liability, if any information or dispute referred to therein
                 could result in a Default or an Event of Default;

                               (v)         As soon as possible and in any event
                 within 10 days after Guarantor knows that any Reportable Event
                 has occurred with respect to any Plan of Guarantor, a
                 statement, signed by an authorized officer, describing said
                 Reportable Event and the action which Guarantor proposes to
                 take with respect thereto;

                              (vi)         As soon as possible, and in any
                 event within 10 days after receipt by Guarantor, a copy of (A)
                 any notice or claim to the effect that Guarantor or any of its
                 subsidiaries is or may be liable to any Person as a result of
                 the release by Guarantor, any of its subsidiaries or any other
                 Person of any toxic or hazardous waste or substance into the
                 environment, and (B) any notice alleging any violation of any
                 federal, state or local environmental, health or safety law or
                 regulation by Guarantor or any  of its subsidiaries, which
                 could, in either case, cause a Material Adverse Change as to
                 Guarantor; and

                             (vii)         Promptly upon request, such other
                 information concerning the condition or operations of any of
                 Guarantor, its subsidiaries, and its Affiliates, financial or
                 otherwise, as Lender may from time to time reasonably request.





                                      -6-
<PAGE>   7
                 (b)           (i)         shall cause to be done all things
                 necessary to preserve and keep in full force and effect
                 Guarantor's existence as a corporation;

                              (ii)         shall comply with the requirements
                 of all applicable Laws and orders (including but not limited
                 to the FDA Act, ERISA and environmental laws) of Tribunals or
                 other governmental authorizations necessary to the ownership
                 of Guarantor's properties or to the conduct of its business if
                 the result of failure to so comply would have a Material
                 Adverse Effect as to Guarantor; and

                             (iii)         will, on request of Lender, promptly
                 correct any defect, error or omission which may be discovered
                 in the contents of any of the Loan Papers to which it is a
                 party or in the execution or acknowledgment thereof, and will
                 execute, acknowledge and deliver such further instruments and
                 do such further acts as may be necessary or as may be
                 requested by Lender to carry out more effectively the purposes
                 of this Guaranty and the Loan Papers to which it is a party.

         11.     Setoff.  Guarantor grants to Lender a right of setoff and Lien
upon each deposit account (time, demand, special and other) of Guarantor
maintained with Lender and any of its Affiliates to secure performance of
Guarantor's obligations hereunder.  If an Event of Default exists, Lender may
setoff and otherwise apply any and all amounts in any such deposit account to
all amounts due hereunder.

         12.     Benefit; Binding Obligation.  This Guaranty is for the benefit
of Lender and its successors and assigns, and in the event of an assignment of
the Guaranteed Indebtedness, or any part thereof, the Rights and benefits
hereunder, to the extent applicable to the Guaranteed Indebtedness so assigned,
may be transferred with such indebtedness.  This Guaranty is binding not only
on Guarantor, but on its successors and assigns.

         13.     Defenses.  The Guaranteed Indebtedness shall not be reduced,
discharged, or released because or by reason of any existing or future offset,
claim or defense of Borrower or any other Person against Lender or against
payment of the Guaranteed Indebtedness, whether such offset, claim, or defense
arises in connection with the Guaranteed Indebtedness or otherwise.

         14.     Change of Borrower Status.  Should the status of Borrower
change through merger, consolidation, or otherwise, this Guaranty shall
continue and shall cover Guaranteed Indebtedness under the new status.

         15.     Fees.  Guarantor agrees to pay reasonable attorneys' fees and
collection costs if this Guaranty is placed in the hands of an attorney for
collection.

         16.     Governing Law.  This Guaranty shall be governed by and
construed according to the substantive Laws of the State of Texas.  The
unenforceability or invalidity, as determined by a court of competent
jurisdiction, of any provision of this Guaranty shall not render unenforceable
or invalid any other provision of this Guaranty.





                                      -7-
<PAGE>   8
         17.     Waiver of Subrogation.  Guarantor shall not assert, enforce,
or otherwise exercise (i) any right of subrogation to any of the rights or
liens of Lender or any other beneficiary of any Lien against Borrower or any
other obligor on the Guaranteed Indebtedness or any collateral or other
security, or (ii) any right of recourse, reimbursement, contribution,
indemnification, or similar right against Borrower or any other obligor on all
or any part of the Guaranteed Indebtedness or any guarantor thereof, and
Guarantor hereby waives any and all of the foregoing rights and the benefit of,
and any right to participate in, any collateral or other security given to
Lender or any other beneficiary of any Lien to secure payment of the Guaranteed
Indebtedness.  The provisions of this Section 17 shall survive the termination
of this Guaranty, and any satisfaction and discharge of Borrower by virtue of
any payment, court order, or Law.

         18.     LOAN PAPERS.  THIS GUARANTY AND THE OTHER LOAN PAPERS
REPRESENT THE FINAL AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED
BY EVIDENCE OF PRIOR, CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS OF THE
PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

         EXECUTED as of March 31, 1995.

                                      NEUROMED, INC.
                                      
                                      
                                      By: /s/ F. ROBERT MERRILL III       
                                          -------------------------------------
                                          F. Robert Merrill III, Vice President





                                      -8-
